2-D particle tracking to determine transport characteristics in rivers with dead zones

Abstract

A Lagrangian-Particle-Tracking-Method (LPTM) has been developed to determine the influence of dead water zones on the transport characteristics in natural rivers. Hereby, the local processes at single dead water zones have been investigated with the help of laboratory experiments. The resulting information, such as storage time, velocity distribution, and distribution of the diffusivity has been implemented into the LPTM. The method has been tested by comparing the results of the simulation with analytical solutions to the one-dimensional advection-diffusion equation. It could be shown that in the presence of large dead water zones at the river banks, an equilibrium between longitudinal shear and transverse diffusion can be reached if the morphologic conditions do not change. The simulations are leading asymptotically to a Gaussian distribution of the cross sectional averaged concentration in longitudinal direction. The transport velocity resulting from LPTM corresponds to the transport velocity predicted by the one-dimensional dead-zone-model only for certain geometrical conditions, which correspond to a fixed exchange coefficient. The transverse distribution of tracer material is influenced by the presence of dead water zones.